Process for preparing a sulfate ester of a polyhydroxy polymer

ABSTRACT

A process for preparing a cellulose sulfate ester by reacting a hydrated cellulose containing about 4 to about 12 percent by weight of water with dinitrogen tetroxide or nitrosyl chloride in the presence of a proton acceptor and a reaction solvent which is a swelling or solubilizing agent for a reaction product. Alternatively, the cellulose reactant may contain less than about 4 percent by weight of water by washing hydrated cellulose containing in excess of 4 percent of water with a highly polar aprotic solvent to reduce the water content. 
     A process for simultaneously preparing a sulfate ester of cellulose and an alkyl nitrite by reacting a nitrite ester of cellulose with sulfur trioxide or a complex thereof to obtain a mixed nitrite:sulfate ester which is reacted with an organic alcohol containing up to about 10 carbon atoms. 
     A process for simultaneously preparing a sulfate ester of cellulose and a mixture of an organic nitrite and an inorganic nitrate by reacting a cellulose nitrite ester with sulfur trioxide or a complex thereof to obtain a mixed nitrite:sulfate ester in the presence of dinitrogen tetroxide with water then being added and neutralizing by addition of a base.

This application is a division of my co-pending application Ser. No.669,483, filed Mar. 23, 1976, U.S. Pat. No. 4,035,569, which is acontinuation of my application Ser. No. 487,196, filed July 10, 1974,abandoned, which is a continuation-in-part of my application Ser. No.298,580, filed Oct. 18, 1972, abandoned which is in turn acontinuation-in-part of my application Ser. No. 40,442, filed May 25,1970 and entitled "NITRITE, NITRATE AND SULFATE ESTERS OF POLYHYDROXYPOLYMERS," now U.S. Pat. No. 3,702,843.

Ester derivatives of polyhydroxy polymers are known and have beendescribed extensively in the prior art literature. The chemical andphysical properties of such ester derivatives depend to a large extenton the particular nature of the polymer, its molecular weight, the typeof ester substituent group, and the degree of substitution of thepolymer (hereinafter referred to as D.S.). Due to the manner in whichester derivatives of polyhydroxy polymers have previously been prepared,the D.S. of the resulting ester derivatives has not been relativelyuniform. This has produced ester derivatives whose properties, e.g.,water solubility and compatibility with various metallic ions, have notbeen generally satisfactory and has restricted the use areas for theester derivatives.

In accord with the present invention, it has been found that esterifiedpolyhydroxy polymers having novel and unusual properties may be preparedfrom nitrite esters of the polyhydroxy polymers. The nitrite esters areemployed in the present invention as reaction intermediates because ofthe instability of the nitrite ester groups and the solubility of theester in the reaction medium. Through use of the nitrite esterintermediates, polymeric products, such as nitrate esters or sulfateesters of polyhydroxy polymers, are obtained which have novel propertiesand a generally uniform substitution of nitrate or sulfate ester groupsamong the polymer units. Due to the relative instability of the nitriteester groups, polyhydroxy polymer nitrites may be used also for makingfilms, fibers and other shaped articles consisting of homogeneousmixtures of various polyhydroxy polymers or of one or more polyhydroxypolymers and one or more other polymers.

In the formation of an ester derivative of a polyhydroxy polymeraccording to the present invention, the amount of depolymerizationresulting from the reaction is negligible. Thus, products are obtainedwhich have very high solution viscosities. In the case of sulfate estersof polyhydroxy polymers, I have obtained, for example, products whosesolution viscosities are many times greater than the solutionviscosities of superficially similar sulfate esters produced by priorart methods.

In addition, it is possible according to the invention to produceesterified polyhydroxy polymers which have D.S. values that cannot beobtained by previously known methods. As an example, I have preparedcellulose sulfate esters having a low D.S., e.g., less than about 0.3 inwhich the ester groups are substantially uniformly distributed among thecellulose polymer units. Also, I have obtained sulfuric acid esters oflocust bean gum and guar gum which have a D.S. of above 1. Stillfurther, I have prepared water soluble nitrate esters of polyhydroxypolymers having a D.S. of less than 1. The properties of these nitrateesters are especially surprising since previous nitrate esters ofpolyhydroxy polymers have, in general, been highly substituted andinsoluble in water.

The relatively uniform distribution of the ester substituent groups overthe macromolecule obtainable according to the invention results, inpart, from the fact that the polymeric nitrite intermediate used in thereaction is solvated or even dissolved in the reaction medium. Incontrast, in prior art methods, the polymeric starting material wasgenerally suspended in the reaction medium in the form of insolubleparticles. The homogeneity of the products prepared according to thepresent invention is of particular importance when the D.S. of theesterified products is considerably below the maximum D.S. for theparticular polyhydroxy polymer, such as in the sulfate esters of theinvention and particularly in the case of the cellulose sulfate esters.For example, in previous sulfation procedures, e.g., in preparation ofcellulose sulfate esters, insoluble cellulose fiber was used as thestarting material. In sulfating the fiber, the reaction mechanisminvolved the so-called "Peeling Process", in which the fiber surface wasfirst partially substituted, then solvated and removed by the reactionmedium, and then highly substituted by reaction with excess sulfationreagent in the reaction medium. During the "Peeling Process," the nextinner layer of the cellulose fiber was then exposed and sulfated in asimilar fashion with the process proceeding until most of the fiber orthe sulfation reagent was consumed.

As a result of the "Peeling Process", the polymeric sulfates which werepreviously obtained were highly substituted and had a D.S. relativelyclose to the maximum for the polymer irrespective of the amount ofsulfation reagent employed. Even when the average D.S. of the polymerwas less than the maximum D.S. of the polymer, the distribution of estersubstituent groups was not uniform and a considerable number of thepolymer units were fully substituted while other polymer units had avery low D.S. or were not substituted at all. These drawbacks areprevented by the present invention since the nitrite ester used as anintermediate is solvated or solubilized and the ester substituent groupsin the final product are, thus, distributed substantially uniformlyamong the polymer units of the product. Thus, in cellulose sulfateproducts of the invention having a D.S. of 2 or 1, substantially all ofthe polymer units in the cellulose will contain only two sulfate estergroups or one sulfate ester group.

Due to the substantially uniform distribution of ester groups among thepolymer units in the products of the present invention, the productshave, in general, unusual solubility characteristics. Also, solutions ofthe products have unusual compatibilities with metallic ions. Forexample, cellulose sulfate products provided according to the inventionwhich have a D.S. of about 0.3 to about 1 are soluble in water. This isquite surprising since the prior literature reports that colloidalcellulose sulfate must have a D.S. in excess of 1 in order to be watersoluble.

In addition, sulfate esters of polyhydroxy polymers of the presentinvention are also markedly different from superficially similarmaterials of the prior art in terms of their compatibilities with a widevariety of metallic ions and also their compatibilities with relativelyhigh concentrations of metallic ions. Still further differences areobserved between the products of the present invention and superficiallysimilar materials of the prior art, e.g., sulfates of polyhydroxypolymers, in terms of reactivity with water soluble proteins.

As disclosed in my prior copending application Ser. No. 298,580, oneaspect of the present invention is directed to a process for thepreparation of nitrate esters or sulfate esters of a polyhydroxy polymerwhich is a polysaccharide or a polyvinyl alcohol that is partiallysubstituted with ether or ester groups. Etherified and esterifiedpolysaccharides or polyvinyl alcohol are known materials which mayinclude, for example, substituent groups such as formate, acetate,carboxymethyl, methyl ether, ethyl ether, and propionate groups. Typicalof the known etherified and esterified materials which may be employedas starting materials are carboxymethyl cellulose, methyl cellulose,hydroxyethyl cellulose, alginic acid acetate, alginic acid propionate,starch phosphate, hydroxypropyl guar, pectic acid butyrate,carboxymethyl starch, partially hydrolyzed polyvinyl acetate, naturalsulfate esters such as carrageenan, natural acetyl esters such as gumkaraya and xanthan gum, etc.

In the formation of nitrate or sulfate esters of etherified oresterified polysaccharides or polyvinyl alcohol, according to thepresent invention, it is necessary that the reactant materials containfree hydroxyl groups. Thus, the etherified or esterified polysaccharideor polyvinyl alcohol used as the starting material is only partiallysubstituted and contains free hydroxyl groups which are utilized asreactant sites in accord with the invention. The free hydroxyl groups onthe etherified or esterified starting materials may, thus, benitrosated, nitrated and also sulfated in a manner similar to thenitrosation, nitration, and sulfation of the unsubstituted polyhydroxypolymers to provide the corresponding ester derivatives of the partiallyetherified or esterified polyhydroxy polymers.

The nitrite esters of polyhydroxy polymers, employed as reactionintermediates in the present invention, are prepared by nitrosating asuspension of the desired polyhydroxy polymer starting material in asuitable organic solvent at a reaction temperature of below about 50° C.The nitrosating reactant is preferably dinitrogentetroxide which is inequilibrium with its monomer nitrogen dioxide. Through use of thenitrite ester as a reaction intermediate, nitrate and sulfate esters ofpolysaccharides and polyvinyl alcohol can be readily synthesized inaccord with the present invention. The resulting nitrate and sulfateester products show a negligible degree of depolymerization and aselective degree of esterification. Also, the nitrate and sulfate esterproducts are distinguished by their homogeneity of substitution, i.e.,the ester groups, such as sulfate ester groups, are relativelyhomogeneously distributed over the macromolecule. Thus, the propertiesof the products differ substantially from the properties ofsuperficially similar products of the prior art in providing higherviscosities and in being compatible with certain metallic ions.

Water soluble nitrate esters may be easily prepared from thecorresponding nitrite esters in accord with the invention by simplyheating the solvated nitrite esters in the presence of nitric acid andremoval of residual nitrite groups by treatment with a protic solvent.The resulting nitrate ester product is soluble in water, is relativelyundegraded, and its aqueous solution also tolerate relatively largeamounts of water miscible organic solvents.

Polymeric sulfate esters are also prepared in accord with the presentinvention by sulfating the nitrite ester of a polysaccharide orpolyvinyl alcohol with sulfur trioxide or a complex thereof at arelatively low reaction temperature. Thereafter, residual nitrite estergroups are removed from the polymer by reaction with a protic solvent toprovide a relatively undegraded polymeric sulfuric acid ester. Thesulfuric acid ester may then be neutralized or made slightly alkaline toprovide the more stable salt form of the ester. The undegraded alkaliester salts are highly soluble and their aqueous solutions possess ahigh viscosity. Thus, the sulfate ester salts are useful as thickenersin aqueous media.

Typical of known polyhydroxy polymers which may be utilized as startingmaterials are the polysaccharides such as cellulose, starch,hemicellulose, guar gum, locust bean gum, gum arabic and the mannans;the polyuronic acids typified by alginic and pectic acids, and thesynthetic polyhydroxy polymers such as polyvinyl alcohol. In accord withone aspect of the invention, the partially etherified or esterifiedpolyhydroxy polymers, as described previously, are used as startingmaterials in the preparation of nitrate esters or sulfate esters of thepartially substituted polyhydroxy polymers.

The starting polyhydroxy polymer is suspended in a suitable solventwhich includes a swelling or solubilizing agent for the polymericreaction product and a proton acceptor. Solvents which have been foundsuitable in serving both as a proton acceptor and a swelling orsolubilizing agent include weak tertiary amine base as typified bypyridinde, quinoline and isoquinoline and also N,N-dialkyl acylamidessuch as N,N-dimethylformamide and N,N-dimethylacetamide (hereinafterreferred to as DMF and DMAC respectively), and mixtures thereof.Suitable swelling or solubilizing agents are generally solvents whichare capable of dissolving polymeric esters. Typical examples of suchswelling or solubilizing agents are ethyl acetate, ethyl formate,benzene, acetone, methyl ethyl ketone, and the like and mixturesthereof. Compounds which are suitable as proton acceptors are those, aspreviously described, which are capable of providing both swelling orsolubilizing of the polymeric nitrite ester and also acting as a protonacceptor.

The amount of solvent which may be utilized to suspend the polyhydroxypolymer is not critical and may be varied over a relatively wide range.However, sufficient solvent should be used to avoid difficulty inhandling the resulting viscous mixture. In general, it has been foundthat a minimum solvent to polymer weight ratio is 3:1, i.e., three partsby weight of solvent for each part of polymer.

In general, it is preferable that the solvent be capable of bothswelling or solubilizing the resulting polyhydroxy polymer nitrite esterand also acting as a proton acceptor. The use of a single solvent, asopposed to use of a mixture of a proton acceptor with a swelling orsolubilizing agent, provides process economies since it simplifies therecovery and the reuse of the solvent material. However, should amixture of a proton acceptor with a swelling or a solubilizing agent beemployed, it is necessary that the mixture contain at least one mole ofthe proton acceptor for each mole of the nitrosating agent, e.g.,dinitrogentetroxide.

As stated, when a nitrite ester is nitrated or sulfated in accord withthe invention, the product which is obtained is a novel polysaccharideor polyvinyl alcohol which contains a mixture of nitrite ester groupswith sulfate or nitrate ester groups with the mixture of groups beingsubstantially uniformly distributed among the polymer units in thepolysaccharide or polyvinyl alcohol. These novel products are valuableintermediates in the preparation of a sulfate or nitrate ester of apolysaccharide or polyvinyl alcohol in which the sulfate or nitrateester groups are substantially uniformly distributed among the polymerunits in the polysaccharide or polyvinyl alcohol.

The use of a nitrite ester of a polysachharide or a polyvinyl alcohol asa starting material in the preparation of another ester of apolysaccharide or a polyvinyl alcohol is of particular importance in thepreparation of novel cellulose sulfate esters. By controlling the degreeof substitution of the nitrite ester of cellulose employed as thestarting material, the degree of substitution of the cellulose sulfateproduct may be likewise controlled. Thus, when the nitrite ester ofcellulose has a degree of substitution of 2 to 3; the cellulose sulfateester which is produced in accordance with the invention has a degree ofsubstitution ranging up to about 1.1. However, when the nitrite ester ofcellulose has a degree of substitution which is less than 2, thecellulose sulfate ester has a degree of substitution greater than about1.1. In each case, the sum of the degree of substitution of thecellulose sulfate ester and the degree of substitution of the nitriteester is equal to about 3.0.

A further aspect of the invention concerns novel water soluble sulfateesters of cellulose which have a degree of substitution of about 0.3 toabout 1.0 with the sulfate ester groups being substantially uniformlydistributed among the polymer units of the cellulose. The watersolubility of these materials is quite surprising since cellulosesulfate esters, as prepared by prior art methods, are not water solubleunless the degree of substitution is in excess of 1.0. In the usage ofthese water soluble sulfate esters of cellulose, a further aspect of theinvention concerns a thickened aqueous medium which contains water and awater soluble sulfate ester of cellulose having a degree of substitutionof about 0.3 to about 1.0 with the sulfate ester groups beingsubstantially uniformly distributed among the polymer units of thecellulose and the cellulose sulfate ester being present in an effectiveamount to thicken the aqueous medium.

A still further aspect of the invention concerns water insoluble estersof cellulose which are, however, highly swellable in the presence ofwater. These water insoluble cellulose sulfate esters have a degree ofsubstitution of less than about 0.3 with the sulfate ester groups beingsubstantially uniformly distributed among the polymer units of thecellulose. The water swellability of these materials is quite unusual.Due to the unusual properties of the water swellable esters of cellulosehaving a D.S. less than about 0.3, these materials have novel utilitiesin the preparation of absorbent materials, such as diapers, towels andthe like.

A further aspect of the invention concerns nitrite esters of apolysaccharide or polyvinyl alcohol having a degree of substitution ofless than about 2.0. In particular, the nitrite esters of cellulosehaving a degree of substitution of less than 2.0 are of unique valuesince they may be employed in forming cellulose sulfate esters, asdescribed, having a degree of substitution of about 1.1 to 2.0 with thesum of the degree of substitution of the nitrite ester groups and thedegree of substitution of the sulfate ester groups in the precursormixed ester being equal to about 3.0.

A still further aspect of the invention concerns novel water solublenitrate esters of a polysaccharide or a polyvinyl alcohol having adegree of substitution of less than 1.0 in which the nitrate estergroups are substantially uniformly distributed among the polymer unitsof the polysaccharide or polyvinyl alcohol. The properties of thesematerials are unique in that nitrate esters produced by prior artprocedures are highly substituted and water insoluble.

As a corollary to my unique water soluble nitrate esters of apolysaccharide or a polyvinyl alcohol, a further aspect of the inventionconcerns a thickened aqueous medium containing water and a water solublenitrate ester, as described, having a degree of substitution of lessthan 1.0. The nitrate ester groups are substantially uniformlydistributed among the polymer units of the polysaccharide or polyvinylalcohol and the water soluble nitrate ester is present in an effectiveamount to thicken the aqueous medium.

A still further aspect of the invention concerns as improved process forthe preparation of nitrite esters of cellulose. As described, the usageof a nitrite ester intermediate of cellulose makes possible thepreparation of novel cellulose esters, such as cellulose sulfate orcellulose nitrate, in which the properties of the final product may beattributed to the substantially uniform distribution of ester groupsamong the polymer units of the cellulose. It has been found that thenitrosation of cellulose with dinitrogentetroxide or nitrosyl chloride,and the subsequent sulfation as described previously, may be evenfurther improved if the cellulose reactant is in an activated state orsuitably activated. In accord with the improved process, the cellulosereactant is in a hydrated form and contains from about 4 to about 12percent by weight of water with the water being substantially uniformlydistributed throughout the cellulose reactant.

In using the hydrated cellulose as a reactant, the nitrosation reactioncan be carried out in a shorter time with the use of essentiallystoichiometric amounts of the nitrosation reactant. This produces a morehomogeneous reaction mixture, a higher clarity product and, thus,permits easier separation of the product from the reaction mixture andreduces the need for filtration.

A still further aspect of the invention concerns a variation of myimproved nitrosation process in which the cellulose reactant issubstantially uniformly hydrated. In this variation, a hydratedcellulose which may contain in excess of about 4 percent by weight ofwater distributed substantially uniformly throughout the cellulose iswashed with a highly polar aprotic solvent to reduce the water contentof the cellulose to less than about 4 percent by weight. Surprisingly,it has been found that the cellulose remains in an activated state afterwashing with the aprotic solvent, even though the washed cellulose has awater content less than about 4 percent by weight. The washed cellulosecan then be employed in the manner described previously for nitrosationwith dinitrogentetroxide or nitrosyl chloride.

In a still further aspect of the invention, it has been found that thenitrite substituent groups present in nitrite esters of polyhydroxypolymers, e.g., cellulose, or in mixed nitrite:nitrate esters ornitrite:sulfate esters of a polyhydroxy polymer are surprisingly labile.Thus, unlike other nitrites, the nitrite substituent groups on thecellulose (or other polyhydroxy polymer) may be readily removed to formalkyl nitrites during formation of nitrate or sulfate esters ofcellulose from cellulose nitrite esters with the alkyl nitrites beingby-products to the formation of cellulose nitrate or cellulose sulfateesters.

In forming an alkyl nitrite ester as a by-product in accord with theinvention, an alkyl alcohol is added to a reaction mixture containing amixed nitrite:nitrate or a mixed nitrite:sulfate ester of apolysaccharide or a polyvinyl alcohol. Since the mixed ester isgenerally formed through addition of a nitrating or sulfating reagent,as described previously, to a reaction mixture formed in the productionof the nitrite ester intermediate, dinitrogentetroxide may be liberatedand be present in the reaction mixture. When alkyl alcohol is added, thealcohol reacts with both the free dinitrogentetroxide and the labilenitrite groups on the polysaccharide or polyvinyl alcohol. The reactionof the dinitrogentetroxide with the alkyl alcohol results in theformation of alkyl nitrite esters by a direct nitrosation which iscomparable, in terms of mechanism, to reaction of dinitrogentetroxidewith a polysaccharide or polyvinyl alcohol in forming the nitrite ester.However, reaction of the nitrite substituent groups on thepolysaccharide or polyvinyl alcohol with the alkyl alcohol occursthrough a transesterification reaction rather than a direct nitrosation.Although not bound by any theory, it appears that thetransesterification reaction favors the production of the most stablenitrite ester in the system which, in this particular case, is the alkylnitrite which is produced quantitatively.

Whatever the reaction mechanism may be, it is most important that boththe free dinitrogentetroxide and the nitrite substituent groups on thepolysaccharide or polyvinyl alcohol quantitatively form the same alkylnitrite product so that the excess dinitrogentetroxide enters into theproduction of the valuable by-product alkyl nitrite.

As a suitable alkyl alcohol, various alkanols and alkanediols may beused, such as propanol, butanol, amyl alcohol, ethanediol, 1,2-propanediol, etc. In addition, higher alcohols may be used such asdecanol containing up to about 10 carbon atoms. Primary alcohols, suchas butanol, secondary alcohols, such as isopropanol, and also tertiaryalcohols, such as tertiary butyl alcohol are equally suitable for thereaction. In order to utilize the dinitrogentetroxide reagentquantitatively in the reaction, the alkyl alcohol reactant should bepresent in an amount of at least 1 mole of alkanol or 1/2 mole ofalkanediol for each mole of dinitrogentetroxide which is initially addedin forming the nitrite ester of the polysaccharide or polyvinyl alcoholintermediate with the alcohol being added after formation of the mixedpolysaccharide or polyvinyl alcohol ester.

Since alkyl nitrite esters are relatively stable in comparison to thenitrite esters of polysaccharides or polyvinyl alcohol, the furtherreaction steps in forming the primary nitrate or sulfate ester producti.e., neutralization, separation and isolation of the resulting nitrateor sulfate ester of the polysaccharide or polyvinyl alcohol, can becarried out without first removing the alkyl nitrite ester. Thus, forexample, in forming a mixed nitrite: surfuric acid ester of cellulosewith subsequent addition of the required amount of alcohol, theresulting sulfuric acid ester of cellulose may be precipitated byaddition of acetone to the reaction mixture followed by removal of theprecipitate for further processing. The alkyl nitrite ester remains inthe filtrate and both the solvents and the alkyl nitrite may be readilyrecovered by fractional distillation or any other suitable means. Sincethe filtrate is acidic, it may be neutralized with a suitable base priorto distillation to minimize decomposition of the various compounds. Asan additional way to minimize decomposition, the distillation may becarried out at a reduced pressure.

In separating the ester product, such as the sulfuric acid ester ofcellulose, it is generally preferred to neutralize the entire reactionmixture without first isolating the ester product. This provides a largesaving in the amount of solvent which is used and no decomposition ofthe alkyl nitrite by-product has been observed when the product recoveryis carried out in this manner. Thus, after addition of the alkanol oralkanediol, a suitable base, such as the ammonium and N-substitutedammonium, alkali, or alkaline earth hydroxides, carbonates, orbicarbonates is added as an aqueous solution or as a suspension of anexcess quantity of base in its saturated solution with continuous mixingof the reaction mixture during addition of the base. The preferred basesare the alkali carbonates and alkali bicarbonates which may be addedalso in the form of dry powders. To prevent any degradation of thepolysaccharide ester product or polyvinyl alcohol ester product, e.g.,the cellulose sulfate ester, the reaction mixture is preferably kept ata temperature of below about 15°-20° C. until the neutralization iscompleted.

If the solids concentration of the reaction mixture is sufficiently highand the concentration of water in the mixture is relatively low, thecellulose sulfate ester may be present in a wet solid form and may bereadily removed. If, however, the cellulose sulfate ester is in the formof a paste after neutralization, a sufficient quantity of a watermiscible solvent, such as acetone, methanol, ethanol, or isopropanol, isadded to cause separation so that the product can be removed, pressedout, and dried or purified further. If the product is dried directly,the resulting product is a technical, relatively crude grade productwhich contains salt as the principal impurity. A purified product may beprepared by extracting the wet solids one or more times with an aqueousalcohol, such as methanol, ethanol, or isopropanol containing about20-40 percent by weight of water, followed by drying of the product atan elevated temperature. Of course, it is also possible to extract thedried technical grade product with aqueous alcohol to arrive at arefined grade.

The filtrate, as described above, may contain both solvents and also analkyl nitrite and both the solvents and alkyl nitrite may be easilyrecovered by distillation. If a higher alkyl nitrite, e.g., in excess ofabout 7 carbon atoms, is produced as by-product which contains arelatively high number of carbon atoms, part of the higher alkyl nitritemay remain with the solids because of its reduced solubility in aqueousalcohol. In this event, a final extraction may be carried out withanhydrous alcohol or with an alcohol containing less than about 20% ofwater. This will remove the higher alkyl nitrite more thoroughly andwill result in obtaining higher yields during distillation. In addition,it is also possible to dry the solids in a closed system such that allabsorbed solvents, including any retained alkyl nitrite, can berecovered.

A second by-product which may be formed in equivalent amounts is aninorganic nitrate, for example, sodium nitrate, if sodium hydroxide orsodium carbonate was used for neutralization. If it is not desired thatan alkyl nitrite ester be produced simultaneously with production of theinorganic nitrate, an equivalent amount of water may be added to thereaction mixture instead of adding an alkyl alcohol. This will thenresult in the formation of equivalent amounts of inorganic nitrate andnitrite, such as sodium nitrate and sodium nitrite. Both salts will bein the filtrate and will remain in the residue after recovery of thesolvents. The salts may be purified by crystallization or other knownmethods to provide salts of medium or high purity. However, if the saltsare to be used as fertilizers, additional purification may not benecessary.

The first step of a process in accordance with one embodiment of thisinvention comprises nitrosating a polyhydroxy polymer suspended in asuitable solvent with dinitrogentetroxide, nitrosyl chloride or mixturesthereof to obtain the corresponding polyhydroxy polymer nitrite ester.

The nitrosating compound is used in the reaction mixture at a molarratio of anhydroglucose or generally polymer unit to dinitrogentetroxideor nitrosyl chloride of about 1:0.1 to 1:3, resulting in a D.S. of 0.1to 3. Since the reaction is quantitative, the D.S. approximatelycoincides with the molar amount of nitrosating agent used. If nitrosylchloride is used in combination with DMF or DMAC, a 2.5 to 3.0-foldexcess of the nitrosating reagent is required to attain these D.S.'s.Stated another way, one mole of dinitrogentetroxide or nitrosyl chlorideis necessary to replace one mole of hydroxyl radical of the polyhydroxypolymer, and if nitrosyl chloride is used with an N,N-dialkyl acidamideas the proton acceptor, 2.5-3.0 moles of nitrosyl chloride are required.

The maximum D.S. for hexosans, such as cellulose, starch, guar andlocust bean gums, mannans, and the like is about three; for pentosans,such as hemicellulose, and polyuronic acids, such as alginic and pecticacids, it is about two; and for polyvinyl alcohols the maximum D.S. isabout one or less. Thus, the molar amount of dinitrogentetroxidenecessary to obtain complete esterification for hexosans is about threemoles per mole of anhydrohexose unit, for pentosans and polyuronic acidsabout two moles per mole of anhydropentose or uronic acid units, and forpolyvinyl alcohols about one mole or less depending upon the degree ofsaponification of the starting compound. The same mole ratio amount ofnitrosyl chloride is necessary for complete esterification of each ofthe hereinbefore described classes of polyhydroxy polymer unless DMF orDMAC is used as the solvent, in which case the amount has to besubstantially tripled. An excess amount of the nitrosating compoundbeyond that necessary for complete esterification may be added with theonly effect being an increased rate of esterification.

The nitrosation reaction is preferably carried out with constantagitation of the reaction mixture. It is necessary that the nitrosatingcompound be introduced into the polymer suspension under the exclusionof moisture. It is preferably to cool the reaction vessel in an ice bathor the like since the reaction is moderately exothermic, and it isdesirable to maintain the temperature of the reaction mixture below 50°C.

If maximum esterification is desired, completeness of the reaction isindicated by the formation of a clear solution or paste, while partialesterification is indicated by a swelling and/or partial dissolving ofthe product in the reaction mixture.

The polymeric nitrite esters are relatively sensitive products anddecompose immediately upon addition of a protic solvent, such as water,methanol, ethanol, isopropanol, or the like in the presence of a mineralacid catalyst. This results in the regeneration of the undegradedpolyhydroxy polymer starting material.

Since the novel polymeric nitrite esters of this process find theirprimary utility as intermediates in the production of other esterderivatives, such as polymeric nitrate and sulfate esters and the like,there is no need to isolate the nitrite esters as the reaction mixturemay be used for those processes, as hereinafter described. However, thepolymeric nitrite esters may be isolated by neutralizing the reactionmixture by the addition of a base, such as mono-, di-, andtrialkylamines, pyridine, alkali or alkali earth metal hydroxides,carbonates, bicarbonates, or the like. The addition of such a base isnecessary only if an N,N-dialkyl acylamide had been used as the protonacceptor since, during nitrosation with dinitrogentetroxide or nitrosylchloride, an equimolar amount of nitric acid or hydrochloric acid isformed. If a weak tertiary amine base, such as pyridine or quinoline,had been used as the proton acceptor, the addition of a base isunnecessary since, then, the acid formed is neutralized by the tertiaryamine base and cannot serve as a catalyst for the decomposition of thepolymer nitrite.

The neutralized, or preferably slightly alkaline solution is then addedto ice cold water with stirring to separate the polymeric nitrite esteras a fibrous material, which may be easily removed. Those products witha D.S. considerably below the maximum may be swellable or even solublein water, in which case an alcohol is used in place of the water.

The isolated product is relatively unstable and for storage purposes itis preferred that it be solvated in a suitable solvent such as benzene,ethylacetate, ethylene dichloride, DMF, DMAC, or the like and stored atlow temperature, preferably below 10° C.

In forming a nitrate ester product, the second step of the processcomprises heating the polymer nitrite ester solution in the presence ofnitric acid with agitation at a temperature of 60°-110° C. for a periodof 15 minutes to about two hours to obtain the corresponding polymernitrate ester.

Although the polymeric nitrite ester solution used in step 2 isgenerally the reaction mixture formed in step 1, in which DMF or DMAChas been used as the proton acceptor and dinitrogentetroxide as thereagent in an amount sufficient for nitrosation to about the maximumD.S., the polymeric nitrite ester may be isolated after step 1 and thenredissolved in one of the solvents, as stated above, and thecorresponding amount of anhydrous nitric acid added. The use of thereaction mixture of step 1 for step 2 obviates the need for isolation ofthe polymeric nitrite ester as hereinbefore described. Also, theaddition of nitric acid during step 2 is not necessary in this casesince, during nitrosation with dinitrogentetroxide in DMF or DMAC,enough nitric acid is formed for the subsequent nitration.

Subsequent to heating, the polymeric nitrate ester is isolated bypouring the reaction mixture slowly and with agitation into two to fivevolumes of a water miscible protic solvent, such as methanol, ethanol,isopropanol, and the like, which splits off residual nitrite groups andseparates the resulting product. The product is then filtered off,washed with fresh solvent and dried.

The resulting nitrate ester product is water soluble, and aqueoussolutions of the ester tolerate relatively high concentrations of watermiscible organic solvents such as the alcohols and ketones. Cellulosenitrate becomes water soluble if the D.S. exceeds about 0.5. Toillustrate, if the D.S. of the cellulose nitrate ester is lower thanabout 0.5, the product can be highly hydrated but does not completelydissolve. Further, the solutions of the polymeric nitrate esters have arelatively high viscosity and owing to their solubility or improvedhydration in water and aqueous organic solvents, their usefulness isenhanced.

To form the polymeric sulfate ester, step 2 as previously defined isomitted and alternatively, the next process step comprises sulfating thepolymeric nitrite ester solution, preferably with a sulfur trioxidesolvent complex, at a low temperature to obtain a polymeric mixednitrite:sulfuric acid ester.

The polymeric nitrite ester solution preferably comprises the reactionmixture of step 1, in which a N,N-dialkyl acylamide has been used as theproton acceptor. The temperature of the reaction mixture should bemaintained in the range from about 0° C.- 25° C., and preferably 5°-15°C. to prevent depolymerization of the molecule during sulfation.

The preferred sulfating agent is sulfur trioxide which may be added tothe reaction mixture in either its liquid or gaseous form or as asolution in an inert solvent such as carbontetrachloride. However, sincethe addition of sulfur trioxide is very exothermic and a low reactiontemperature is critical to obtaining the desired viscosity in theproduct, the sulfur trioxide must be added slowly with stirring, whilemaintaining the reaction mixture in a cooling medium such as an icebath.

In practice, it is preferred that the sulfating agent be first to asolvent, preferably the same solvent as contained in the reactionmixture to facilitate solvent recovery, to form a complex which uponaddition to the reaction mixture produces a less exothermic reaction.Examples of solvents capable of forming a complex with sulfur trioxideare DMF, DMAC, dioxane and pyridine. Generally, the mole ratio of thesulfur trioxide to the solvent in the complex is 1:1. However, it ispreferable to use an excess of the solvent to obtain a suspension orsolution of the complex in the excess.

The complex is slowly added to the reaction mixture with agitation andexclusion of moisture. The amount of sulfating agent to be added to themixture is dependent upon the D.S. desired in the resulting product. Alow D.S. value ranging between 0.1 to 1.0 requires about 0.1 to about1.0 mole of sulfur trioxide per mole of anhydroglucose unit. A D.S.value ranging from about 1.0 to about 2.0 requires about 1.0 to 4.0 moleof sulfur trioxide per anhydroglucose unit. A D.S. exceeding 2.0 isdifficult under the reaction conditions, and a large excess of sulfurtrioxide is required.

The addition of the sulfating agent to the polymer nitrite ester mixtureforms a mixed polymeric nitrite:sulfuric acid ester. Although thepolymeric nitrite ester with a maximum D.S. may be used for thesulfation to obtain products with a degree of sulfation of up to about1.1, it is preferred to use the lower D.S. polymer nitrites for economicreasons and particularly where a D.S. of above about 1.1 is desired.Cellulose, for example, can be easily sulfated to a D.S. of betweenabout 1 and 2 only when the degree of nitrosation is between about 2and 1. However, if the degree of nitrosation drops considerably belowabout 1, sulfation becomes increasingly more difficult and incompleteand the distribution of the sulfate groups non-uniform. Generally, thehigher the degree of sulfation desired, the lower may be the degree ofnitrosation such that the mixed polymer nitrite sulfuric acid ester hasa maximum D.S. In other words, the sum of the degree of nitrosation andthe degree of sulfation should be about 3 for the hexosans, about 2 forpentosans and polyuronic acids, and about 1 or less for the polyvinylalcohols.

The next step of the process comprises reacting the mixed polymericnitrite:sulfuric acid ester with a protic solvent to obtain thecorresponding polymeric sulfuric acid ester.

The addition of a protic solvent such as water, methanol and ethanolresults in the production of the pure polymeric sulfuric acid ester. Theprotic solvent replaces the nitrite groups of the product with hydroxylgroups and is added in stoichiometric amounts or an excess thereof.

To isolate the polymeric sulfate ester product, two to four volumes of awater miscible solvent, i.e., acetone, is added to the mixture toseparate the sulfated polymer therefrom. The ester is removed and washedwith fresh solvent, and redissolved in ice water.

The next step of the process comprises neutralizing the polymericsulfuric acid ester with a base to form a salt thereof.

The isolated polymeric sulfuric acid ester will degrade upon storage andtherefore it is preferable to convert it to a neutral salt. Thepreferred bases for neutralizing the sulfate ester are the hydroxides,carbonates and bicarbonates of the alkali and alkaline earth metals,while ammonium hydroxide and the amines are likewise useable for thispurpose. The resulting salt product is isolated by adding theneutralized mixture with agitation to a water miscible solvent such asacetone, methanol, ethanol, and isopropanol or vice versa. The isolatedproduct may be washed with an aqueous solvent and dehydrated by washingwith anhydrous solvent. The separated polymeric sulfate ester salt maythen be removed and dried for storage.

Instead of neutralizing an aqueous solution of the isolated polymericsulfuric acid ester, the polymeric sulfuric acid ester-protic solventreaction mixture of the previous step may be neutralized directly toobtain the polymeric sulfate ester salt. In this case, the base may beadded as an aqueous solution or in its dry form. In the neutralizedmixture, the product may be present in wet, but solid, form and may beremoved directly by centrifugation or filtration, pressed out, and driedto obtain a technical grade product which contains salt impurities. Apure grade or product is obtained by washing the wet product one or moretimes with aqueous alcohol prior to drying. If there is a relativelylarge amount of water in the neutralized mixture, the product may be toosoft to be removed or it even may be partially dissolved. In this case,enough alcohol is added to harden the product somewhat or to precipitateit, so it can then be filtered off or centrifuged.

The product is water soluble and since it does not undergodepolymerization, a 1% aqueous solution produces a very viscous andstable solution. The sodium cellulose sulfate esters become watersoluble if the D.S. exceeds about 0.3 and have viscosity measurement ofas high as 8000- 9000 cps.

As a result of this unique physical property, the products exhibitutility as thickening, suspending and emulsifying agents. Generally, theviscosity decreases somewhat as the D.S. increases simply because of theadditional weight ot the polymer. However, in the application in boneglue it is preferred to use a product having a D.S. of above 1.0 sincein this particular use, best results are obtained with the higher D.S.products.

The following examples illustrate specific preferred embodiments of thisinvention and are not intended to be limiting. All ratios in thefollowing examples as well as in the specification and in the appendedclaims are by weight unless otherwise indicated, and temperatures areexpressed in ° C.

EXAMPLE I A. Preparation of Cellulose Nitrite Ester from Cellulose

20 g. of Whatman cellulose powder, CF.II, was dried overnight at 110° C.and placed in a three neck, round bottom flask equipped with amechanical stirrer and calcium chloride tube. 200 ml ofN,N-dimethylformamide (DMF) was added to the cellulose powder and themixture was stirred at room temperature. With exclusion of moisture,dinitrogentetroxide (N₂ O₄) gas was slowly introduced to the mixtureover a period of two hours. It was observed that the mixture thickenedwith about 7-8 g. of N₂ O₄ and that a transparent viscous mixturewithout any essential development of color was obtained upon introducingapproximately 15 of N₂ O₄. After introduction of approximately 30 g. ofN₂ O₄, the mixture formed a bluish green viscous solution, and onfurther addition of N₂ O₄, the color became a deep green while theviscosity appeared to remain constant.

To a sample of the three solutions, an excess of pyridine was added andthe slighly alkaline mixture was poured with stirring into ice water. Afibrous precipitate was formed, removed, washed with ice water andpressed out, and the temperature was maintained at 0°-5° C. The fibrousprecipitate of the first two samples was found to be swellable and thatof the third sample was found to be soluble in common solvents forpolymer esters including dimethylformamide, dimethylacetamide, benzene,acetone and ethyl acetate. Upon attempting to dry the fibrousprecipitate, the product decomposed as indicated by the release of brownfumes. The resulting dried product was found insoluble in the abovedescribed common polyner ester solvents.

To identify the resultant products as cellulose nitrite esters and thedegree of substitution or esterification (D.S.) thereof, the productswere decomposed and cellulose and nitrous acid determinations were made.Products isolated from the above three solutions were washed with icewater and suspended in distilled water in a closed Erlenmeyer flask,acidified with sulfuric acid, and magnetically stirred at roomtemperature for 1 hr. The mixture was then neutralized with sodiumhydroxide and the insoluble cellulose was regenerated, filtered off,washed with distilled water and dried in vacuo at 100° C. The filtratewas collected for testing, as hereinafter described.

The identity of the regenerated cellulose was determined by comparisonof the regenerated cellulose with the starting material by IRspectrophotometry, negative nitrogen analysis and found identical by theKjeldahl method, and the absence of carboxyl groups as determined by themethod of Samuelson and Wennerblom described in "Methods in CarbohydrateChemistry, " Vol. III Cellulose, 1963, p. 34.

To determine the lack of depolymerization of the molecule during thereaction and during storage of the reaction medium, the viscosity of theregenerated cellulose from reaction mixtures kept over various periodsof time, in cuprammonium hydroxide solution was compared with theviscosity of the starting material in the same solution at an identical0.5% concentration. The viscosities were measured with a Cannon FenskeViscometer at 25° C. The results of the test are tabulated in the tableon the following page.

    ______________________________________                                                       Time and Temp.                                                 Material       of Storage   Viscosity, Sec.                                   ______________________________________                                        Starting Cellulose Control      28.8                                          Regenerated Cellulose                                                                         6 hr.   5° C.                                                                          27.0                                          Regenerated Cellulose                                                                         30 hr.  5° C                                                                           28.8                                          Regenerated Cellulose                                                                        120 hr.  5° C                                                                           28.3                                          Regenerated Cellulose                                                                        288 hr.  5° C                                                                           27.8                                          ______________________________________                                    

The nitrite in the filtrate, as hereinbefore described, was determinedby oxidation with permanganate solution to nitric acid. The presence ofnitric acid subsequent to oxidation was established by its determinationas nitron nitrate according to the method of Hick described in Analyst,Vol. 59, pp. 18-25 (1934).

The degrees of substitution were calculated from the weight of thecellulose and the amount of nitrous acid. The degree of substitutioncalculated for the first solution containing about 7-8 g. of N₂ O₄ was0.7; the second solution containing about 15 g. of N₂ O₄ was 1.5 and forthe third solution containing about 30 g. of N₂ O₄ was 2.8.

Results substantially similar to those obtained above are obtained whenthe following starting cellulose materials are substituted for Whatmancellulose powder: cotton linter pulp, celluloses derived from wood orisolated from rice, corn, barley and oat hulls or from bagasse. However,if the foregoing starting materials are used, the amount of DMF usedmust be increased owing to the higher viscosities of the resultingproduct. Partially substituted cellulose, such as methyl orcarboxymethyl cellulose can be used also with essentially similarresults except that the amount of reagent required for full nitrosationis less because of the smaller number of free hydroxyl groups present.Likewise, results similar to those obtained above are obtained when thefollowing solvents are substituted for N,N-dimethylformamide:N,N-dimethyl acetamide, pyridine, quinoline, and mixtures thereof, ormixtures of one or more of the foregoing solvents and benzene, ethylacetate, or acetone. It was also found that the dinitrogentetroxide gascould be replaced by its liquid form or a solution thereof in one of theabove solvents and by nitrosyl chloride to produce substantially similarresults.

B. Preparation of Cellulose Nitrate Ester from Cellulose Nitrite Ester

A dry 500 ml. three-neck, round bottom flask was charged with 9 g. ofWhatman cellulose powder, CF II, suspended in 300 ml. of DMF andsolubilized by adding approximately 15 g. of dinitrogentetroxide gas toform cellulose nitrite ester. The cellulose nitrite ester solution wasmechanically stirred and heated at 90° C. for 50 ninutes, poured slowlyand with agitation into about 6 volumes of methanol to form aprecipitate, which was filtered, washed with methanol, and dried.

Upon analysis the precipitate was found soluble in water and upon IRanalysis showed a strong absorption peak at about 1680 cm⁻¹, each testindicative of nitrate ester groups.

Nitrogen determinations by the Kjeldahl method indicated the presence ofnitrogen from which a 0.5 degree of substitution was calculated.

The addition of 15 g. of anhydrous nitric acid or 24 ml. of aceticanhydride to the cellulose nitrite ester solution prior to heatingrevealed that the degree of substitution for the resulting cellulosenitrate ester was elevated to 0.8.

Results substantially similar to those obtained above are obtained whenDMF is substituted by DMAC or by a mixture of DMF or DMAC and benzene orwhen methyl cellulose, carboxymethyl cellulose or carboxyethyl celluloseis used in place of cellulose.

EXAMPLE II A. Preparation of Hemicellulose Nitrite Ester fromHemicellulose

A 500 ml. three-neck round bottom flask equipped with a mechanicalstirrer and calcium chloride tube was charged with 40 g. ofhemicellulose extracted from corn hulls and suspended in 300 ml. of DMF.The suspension was mechanically stirred and under the exclusion ofmoisture, 58 g. of dinitrogentetroxide gas was slowly introduced to themixture at room temperature to form a clear viscous solution ofhemicellulose nitrite ester.

To a portion of the solution was added an excess of pyridine and theslightly alkaline solution was slowly poured with stirring into icewater to separate a fibrous precipitate. The precipitate was removed,washed with ice water and pressed out. The resulting precipitate wasfound soluble in common polymer ester solvents described in Example 1A.Upon drying, the precipitate decomposed releasing brown fumes.

Hemicellulose was regenerated for analysis by slowly adding a portion ofthe remaining hemicellulose nitrite ester solution to four volumes ofmethanol with agitation forming a precipitate which was filtered, washedwith methanol, and dried. The precipitate was identified ashemicellulose by IR spectrophotometry and by negative nitrogen analysisby the Kjeldahl method.

The lack of depolymerization of the regenerated hemicellulose wasdetermined by preparing 2% aqueous solutions of the regenerated productand the starting material and adjusting the pH of the solutions to 6.7with a dilute sodium hydroxide solution. The viscosities of the twosolutions were measured with a Cannon Fenske Viscometer at 25° C. Theviscosity of the regenerated hemicellulose was observed to be 138.5 sec.and the starting material 146.2 sec.

To identify the product as the nitrite ester and to determine the D.S.,an excess of triethylamine was added to the rection mixture and theslightly alkaline solution was poured slowly and with stirring into icewater which resulted in the separation of hemicellulose nitrite ester.The hemicellulose nitrite was removed, suspended in water, and themixture acidified with sulfuric acid and stirred for about 1 hour. Thenit was neutralized with sodium hydroxide and the neutral solution wasadded to 4 volumes of methanol, wherein hemicellulose separated, and wasremoved, washed with methanol, dried and weighed.

The filtrate was collected, the methanol removed by concentration invacuo, and the resulting aqueous nitrite solution was oxidized with apermanganate solution to form nitric acid, the presence of which wasestablished by its determination as nitron nitrate according to themethod of Hick described in Analyst, supra.

The degree of substitution was calculated by the weight of thehemicellulose and the amont of nitrous acid, and was found to be about2.0. With less N₂ O₄, the D.S. was correspondingly lower.

Results substantially similar to those obtained above are obtained whenthe following reagents are substituted for N,N-dimethylformamide:N,N-dimethyl acetamide, pyridine, quinoline and mixtures thereof, andmixtures of one or more of the above solvents and benzene, ethylacetate, or acetone. Likewise, dinitrogentetroxide liquid or nitrosylchloride can be substituted for the dinitrogentetroxide gas to producesubstantially similar results.

Hemicellulose nitrate ester is prepared from the hemicellulose nitriteester in the same manner as related in Section B of Example I.

EXAMPLE III A. Preparation of Starch Nitrite Ester from PregelatinizedStarch

A 500 ml. three-neck round bottom flask equipped with a mechanicalstirrer and calcium chloride tube was charged with 40 g. ofpregelatinized starch and suspended in 300 ml. of DMF. Under exclusionof moisture, approximately 64 g. of dinitrogentetroxide gas was slowlyintroduced to the mixture at room temperature and the mixture wasmechanically stirred to form a clear viscous solution of starch nitriteester.

To test the resulting solution, an excess of pyridine was added to aportion of the solution and the slightly alkaline mixture was slowlypoured with stirring into ice water to separate a fibrous precipitate.The precipitate was removed, washed with ice water and pressed out. Theresulting precipitate was found soluble in the common polymer estersolvents described in Example IA. Upon drying, the precipitatedecomposed releasing brown fumes, indicative of a nitrite. The driedprecipitate was again tested for its solubility, and found to beinsoluble in the common polymer ester solvents.

Another portion of the starch nitrite ester solution was slowly added tofour volumes of methanol with agitation, and the precipitate wasidentified as starch by IR spectrophotometry and by negative nitrogenanalysis by the Kjeldahl method.

The lack of depolymerization of the regenerated starch was determined bypreparing a 1% aqueous solution of the regenerated product and comparingits viscosity against the starting material. The solutions were adjustedto a pH of 6.0 with a dilute sodium hydroxide solution and theviscosities of the two solutions were measured with a Cannon FenskeViscometer at 25° C. The viscosity of the regenerated starch wasobserved to be 29.3 sec. as compared to 30.4 sec. for the startingmaterial.

The product was identified as starch nitrite ester and its D.S.determined by the method described under Example II for hemicellulose.The degree of substitution was calculated by the weight of starch andthe amount of nitrous acid, and found to be about 2.8. The D.S. waslower if a lower amount of dinitrogentetroxide was used for nitrosation.

Results substantially similar to those obtained above are obtained whenthe following starting materials are substituted for the pregelatinizedstarch: alginic acid, guar gum and locust bean gum or starch derivativescontaining free hydroxyl groups, such as hydroxyethyl starch. Likewise,N,N-dimethyl acetamide, pyridine, quinoline and mixtures thereof, andmixtures of one or more of the above solvents and benzene, ethylacetate, or acetone may be substituted for N,N-dimethylformamide toobtain substantially the same results. Further, nitrosyl chloride,liquid dinitrogentetroxide, or a solution of dinitrogentetroxide in oneof the above solvents could be substituted for the dinitrogentetroxidegas and produce substantially similar results.

The starch and other polysaccharide ester solution was converted to thecorresponding nitrate ester solution in a manner similar to Example IB.

EXAMPLE IV A. Preparation of Polyvinyl Nitrite Ester from PolyvinylAlcohol

To a dry 500 ml. three-neck round bottom flask, 10 g. of finely groundpolyvinyl alcohol having a degree of saponification greater than 90% wassuspended in 100 ml. of N,N-dimethylformamide. The mixture wasmechanically stirred and under exclusion of moisture,dinitrogentetroxide gas was introduced. The vessel was cooled with coldwater to keep the temperature at approximately 25° C. A clear viscoussolution was obtained upon the addition of approximately 20 g. ofdinitrogentetroxide gas.

Upon analysis, according to the methods described in Examples II andIII, the resulting product was identified as polyvinyl nitrite esterhaving a degree of substitution of 0.8.

It was found that when the polyvinyl alcohol starting material had adegree of saponification less than 90% for example a product containingabout 50% acetyl groups and 50% free hydroxyl groups, substantially thesame results could be produced as obtained above, however the amount ofdinitrogentetroxide gas required to solubilize the starting material wasless.

The nitrite ester was converted to the nitrate ester in a manner similarto Example IB.

EXAMPLE V A. Preparation of Sodium Alginic Acid Nitrate Ester

2 g. of alginic acid was suspended in 80 ml. of DMF and solubilized by4.5 g. of dinitrogentetroxide gas according to the procedure of ExampleIII. The solution was heated at 90° for 40 minutes and added slowly,with agitation, to 3 volumes ethanol to precipitate alginic acid nitrateester. The isolated precipitate was resuspended in water and neutralizedwith sodium hydroxide. The neutralized solution was then added slowly to3 volumes of ethanol to precipitate sodium alginate nitrate ester.

Results substantially similar to those obtained above are obtained whenpectic acid is substituted for alginic acid. The substitution ofpotassium hydroxide, calcium hydroxide, magnesium hydroxide and ammoniumhydroxide for the sodium hydroxide results in the correspondingpotassium, calcium, magnesium and ammonium salts of the polyuronicnitrate esters.

EXAMPLE VI A. Preparation of Cellulose Sulfuric Acid Ester

10 g. of cotton linter pulp having a high degree of polymerization wassuspended in 500 ml. of DMF and reacted with dinitrogentetroxide to formthe nitrite ester thereof with the maximum D.S. in accordance withExample IA. 40 ml. of DMF containing 3.5 g. of sulfur trioxide was addedto the nitrite ester mixture dropwise over a period of about 40 minutesmaintaining the temperature of the solution at 15° C., with vigorousagitation to form a viscous solution. 20 ml. of water was added to theviscous solution and it was then poured slowly and with vigorousagitation into 3 volumes of acetone to precipitate cellulose sulfuricacid ester, which precipitate was kneaded, washed and acetone, andredissolved in ice water.

B. Preparation of Sodium Cellulose Sulfate Ester

The solution prepared in accordance with Example VIA was neutralized bythe addition of sodium hydroxide to a pH of about 8.0 to form a viscoussolution of sodium cellulose sulfate ester. The solution was addedslowly and with agitation to 3 volumes of acetone to precipitate andisolate the product. The precipitated product was kneaded, collected,washed with fresh acetone and dried. Upon analysis, the yield of sodiumcellulose sulfate ester was 13.9 g. having a degree of substitution of0.65, and a viscosity of 6500 cps. as a 1% aqueous solution.

The viscosity was measured with a Brookfield Viscometer, Model LVT, at12 RPM and 25° C. To determine the degree of substitution, a 0.4 g.aliquot of the product was dissolved in 20% aqueous hydrochloric acidand heated for 15 hours at 100° C. A dark brown solution was formed andfiltered. To the filtrate, an excess of barium acetate was added to theprecipitate sulfuric acid as barium sulfate. The barium sulfate wasdried and weighed and the degree of substitution calculated therefrom.

Results substantially similar to those obtained above are obtained whenthe cotton linter pulp starting material is replaced by cellulose fromother sources and/or having a lower degree of polymerization,hemicellulose, gum arabic, starch, alginic acid, guar gum, locust beangum and polyvinyl alcohol. Other solvents capable of forming a complexwith sulfur trioxide and which may be substituted for DMF in theDMF-sulfur trioxide complex are N,N-dimethyl acetamide, pyridine,trialkylamine, dimethylsulfoxide and dioxane. Likewise, the sulfurtrioxide may be added to the solution in the form of a liquid or a gas,or diluted with an inert solvent such as carbontetrachloride though thereaction is highly exothermic and the use of an ice bath is necessary.

When the above procedure was repeated and the amount of sulfur trioxidewas reduced to 2.5 g., the resulting product had a degree ofsubstitution of about 0.5 and viscosity of about 6000 cps. The yield wasreduced only slightly to 13.4 g.

An increase of the sulfur trioxide to about 4-5 g. and about 6-7 g.resulted in D.S.'s of about 0.7-0.9 and about 1.0-1.1 with viscositiesof about 6000-8000 cps. and about 3000-4000 cps., respectively. However,a further increase of the sulfur trioxide did not result in D.S. valuesof much above 1.0-1.1 under these conditions.

Similar results were obtained when cellulose nitrite ester with a D.S.of 2.4-2.5 was used.

D.S. (Degree of sulfation) values of 1.2-1.3 and about 1.5-1.6 wereobtained by using a cellulose nitrite ester having a D.S. of about1.7-2.0 and about 1.4-1.6 and increasing the amount of sulfur trixoxideto about 8-10 g. and 12-14 g., respectively. The viscosities of 1%aqueous solutions of the products were about 1500- 2000 cps. and about800-1500 cps., respectively. Similar results were obtained with starch,guar and locust bean gums, and with hemicellulose. Also, methylcellulose with a D.S. of about 1.0-1.5, carboxymethyl cellulose, hydroxyethyl starch, acetylated alginic and pectic acids (with a degree ofacetylation of below about 1.5) and hydroxypropyl gear were foundequally suitable for nitrosation and subsequent sulfation. However, theamount of reagent necessary for full nitrosation was based only on thenumber of free hydroxyl groups.

When cotton linter cellulose with a lower degree of polymerization wasused, the D.S.'s were similar but the viscosities were correspondinglylower. Similarly, cellulose from other sources generally producedproducts with lower viscosities.

EXAMPLE VII

Cellulose (25 g.) was suspended in 1000 ml. DMF and about 38 g. N₂ O₄were introduced to obtain cellulose nitrite ester. A solution of acalculated amount of DMF-SO₃ complex in DMF was then slowly added withstirring and cooling to result in a degree of sulfation of about 0.8.

At this stage, a small portion of the mixture was removed, and, afterremoval of the nitrite groups and neutralization, the product wasdialyzed, isolated, and analyzed. The D.S. was found to be 0.8.

The main portion was mixed with the stoichiometric amount of methanolrequired for the quantitative removal of the nitrite groups, andsubsequently another portion of DMF-SO₃ complex, which theoretically wassufficient to increase the D.S. to about 2.0, was added over a period of2 hours. After a total reaction period of about 3 hours, the mixture wasneutralized and the product isolated as described above, dialyzed, andits D.S. determined. The D.S. calculated was 0.8 indicating that nofurther substitution had occurred after removal of the nitrite groups.

Similar results were obtained with guar and locust bean gums. Thisillustrates that sulfation under these conditions does not occur withoutthe prior nitrosation step of this invention.

EXAMPLE VIII

To test the compatibility of the various sodium cellulose sulfate estersof this invention with metal ions, 1% aqueous solutions of the esterswere mixed with the same volume of a 20% salt solution. In cases where20% was above saturation, a saturated salt solution was used.

Products at all D.S. levels were compatible, i.e., no precipitation orgelling occurred, with ammonium sulfate, sodium chloride, potassiumchloride, magnesium chloride, calcium chloride, calcium hydroxide,strontium chloride, strontium hydroxide, aluminum sulfate, sodiumaluminate, zinc sulfate, sodium zincate, nickelous sulfate, cobaltoussulfate, cupric sulfate, cadmium chloride, ferrous sulfate, chromicchloride, lead acetate, mercuric acetate, silver nitrate, stannouschloride, and sodium stannite.

As a simple test for determining compatability with metal ions, a 2%solution of the cellulose sulfate in an aqueous medium may be admixedwith a 2% potassium chloride solution on an equal volume basis afterheating of both solutions to a temperature of about 80° C. After mixing,the mixture may be allowed to cool. The compatibility of the cellulosesulfate with potassium ions is shown by the absence of a precipitate andthe absence of gelation.

Sodium cellulose sulfate esters with a D.S. of about 1.3 and lower werecompatible also with barium acetate, barium hydroxide, cerous chloride,and ferric chloride.

In most cases, the solutions could be saturated with the salt withoutcausing precipitation or gelation.

EXAMPLE IX A. Thickened Rubbing Alcohol Composition

A thickened rubbing alcohol having the following composition isprepared:

    ______________________________________                                        Component           % by Weight                                               ______________________________________                                        Cellulose Nitrate Ester                                                                           5.0                                                       Water               25.0                                                      Ethyl Alcohol       70.0                                                      ______________________________________                                    

The thickened rubbing alcohol exhibits a desired increased viscositywhich tends to slow down evaporation of the alcoholic solution, prolongskin conact and thereby aid absorption.

EXAMPLE X A. Non-running Glue

    ______________________________________                                        Component          Amount by Weight                                           ______________________________________                                        Bone Glue           150.0 g.                                                  Sodium cellulose sulfate                                                                           5  g.                                                    Water              1000  g.                                                   ______________________________________                                    

This improved glue exhibits a higher viscosity tending to retard runningof the glue, particularly on vertical surfaces. The particularcomposition exhibited a viscosity of 1000 cps. at 25° C. and about 300cps. at 50° C. and did not interfere with or change the properties ofthe bonding glue.

Among the other utilities for my cellulose sulfate products are theirapplication in oil well drilling mud as a suspending agent, in secondaryoil recovery through water flooding as a thickener of the water phase,in cosmetics as an emulsifier and emollient, in food products as athickener and stabilizer, in cleaning compositions as a stabilizer andthickener, in wax emulsions, paints, and photographic emulsions, e.g.,for protein reactivity, etc.

EXAMPLE XI

Utilizing the process of the invention as described above, esters ofpolyhydroxy polymers such as polysaccharides, polyvinyl alcohols, andpartially substituted etherified or esterifid polysaccharides andpolyvinyl alcohols which still contain a substantial number of freehydroxyl groups are prepared and the following specific products areobtained thereby:

A. Nitrite esters of polysaccharides, polyvinyl alcohols,polysaccharides partially substituted with stable radicals, andpolyvinyl alcohols partially substituted with stable radicals.

B. Nitrite esters of starch, guar gum, locust bean gum, hemicellulose,gum arabic, mannan, alginic acid and pectic acid having a D.S. between0.1 and the maximum.

C. Nitrite ester of cellulose having a D.S. between about 0.1 and 2.0.

D. Nitrite ester of cellulose having a D.S. between 2.0 and 3.0.

E. Water soluble nitrate esters of polysaccharides and polyvinylalcohols having a D.S. of less than 1.0.

F. Sulfuric acid esters of polysaccharides and polyvinyl alcohols andsalts thereof with a D.S. of below 2.0 and with substantially uniformdistribution of sulfate groups over the macromolecule.

G. Sulfuric acid esters of guar gum and locust bean gum having a D.S. ofbetween 1.0 and 2.0.

H. Sulfuric acid esters of cellulose having a D.S. of between 1.0 and2.0.

I. Water soluble sulfuric acid esters of cellulose having a D.S. between0.3 and 1.0.

J. Sulfuric acid esters of cellulose having a D.S. between 1.0 and 1.3the aqueous solutions of which are compatible and non-gellable in thepresence of potassium, barium, strontium, cerous, aluminum, and ferricions.

K. Sulfuric acid esters of cellulose having a D.S. of less than 2.0 andwith substantially uniform distribution of sulfate groups over themacromolecule, the aqueous solutions of which are compatible andnon-gellable in the presence of potassium, strontium and aluminum ions.

As stated previously, a further aspect of the invention involves the useof an activated cellulose polymer in the formation of a nitrite ester.This aspect of the invention is illustrated in the following Examples inwhich all parts and percentages are by weight unless otherwiseindicated.

EXAMPLE XII

Cotton linter pulp was dried at 100° to 110° C. in vacuo over P₂ O₅ for5 hours; a dried 20 g. portion was placed in a three-neck round bottomflask provided with a calcium chloride tube, a strong stirrer, and adropping funnel, and 1 liter of DMF was added. An amount of 30 g. of N₂O₄ then was introduced with stirring over a period of about 30 minuteswhile the temperature of the mixture was kept below about 30° C. bycooling in a cold water bath. The mixture thickened, but the reactionwas incomplete even after mixing for several hours indicated by thepresence of haze and apparently unreacted fibers. The addition ofanother 3 g. of N₂ O₄ did not result in a substantial improvement.

In isolating and analyzing the resulting cellulose nitrite ester, to asmall portion of the mixture was added an excess of pyridine. Theslightly alkaline mixture was added to ice water, the precipitatecollected, washed with ice water, and pressed out while the temperaturewas kept at about 0° C. The material was redispersed in distilled waterin a closed Erlenmeyer flask and acidified with sulfuric acid. Afterstirring magnetically for about 1 hour, the mixture was neutralized andthe regenerated cellulose removed, washed, dried, and weighed. Thefiltrate was collected quantitatively and the nitrite determined byoxidation with permanganate to nitric acid. The presence of nitric acidsubsequent to oxidation was established by its determination as nitronnitrate according to the method of Hick described in Analyst, Vol. 59,pages 18 - 25 (1934). The degree of nitrosation was found to be about2.7-2.8.

The cellulose nitrite reaction mixture prepared from 20 g. of celluloseand 30 g. N₂ O₄ was sulfated by the slow addition (about 30 min.) of asolution of DMF-SO₃ complex (about 6 g. SO₃) in DMF. The reaction wascarried out with strong stirring and under exclusion of moisture, andthe temperature was kept below about 20° C. The mixture remained hazyand still contained fibers even after mixing for about 1-2 hours. Thereaction mixture was then transferred to a mixer, diluted with about 500ml. of water, and adjusted to a pH of 7-8 by the slow addition of sodiumcarbonate solution. During neutralization, the temperature of themixture was kept below 20°-25° C by the addition of ice. Enoughisopropanol was then added to separate the product, and the product waspressed out, washed twice with aqueous isopropanol, pressed out again,dried in vacuo at 100° C, and milled. The product had a D.S. of about0.6 and a 1% aqueous solution a viscosity of about 3000 cps. (BrookfieldViscometer, LVT Model, 60 RPM) but was somewhat hazy and containedfibers.

In another experiment, 20 g. of anhydrous cotton linter pulp was treatedas described above, but only about 15 g. of N₂ O₄ was used for thenitrosation to result in a D.S. of about 1.5 and an amount of DMF-SO₃complex containing about 12 g. of SO₃ for the subsequent sulfation. Theresults were similar to those above. The cellulose sulfate had a D.S. ofabout 1.5, and a 1% aqueous solution had a viscosity of about 500 cps.but was hazy and contained fibers.

Essentially similar results were obtained when wood cellulose, cellulosefrom vegetable hulls or bagasse, and chemically treated and degradedcellulose, such as Whatman Cellulose Powder were substituted for thecotton linter pulp. However, it appeared that the reaction with WhatmanCellulose Powder proceeded more smoothly and that a solution of itsfinal sulfated product was the least hazy and contained a lesser amountof fibers than those produced from other cellulose types.

Substitution of the DMF in the reaction medium by DMAC or pyridine ormixtures of these compounds did not essentially change these results.Also, no essential differences were noticed when the SO₃ was used as acomplex with other solvents, such as DMAC, dioxane, DMSO, and the like,or when NOCl was used instead of N₂ O₄ provided, however, that the molaramount of NOCl was increased 2.5 to 3 fold.

EXAMPLE XIII

Cotton linter pulp as described in Example XII was suspended in waterand mixed in a Waring Blender for 2 min., pressed out, washed with DMF,and pressed out again. The cellulose then had a water content of about8-10%. A portion of 20 g. of this cellulose then was nitrosated with 30g. of N₂ O₄ as described above. The resulting solution was clear and didnot contain fibers after a reaction time of 20-30 min., and no excess ofN₂ O₄ was required to obtain a quantitative reaction. The sulfation wascarried out as described above and resulted in products formingperfectly clear solutions that did not contain fibers.

Similar results were obtained when the residual water content was 5% and2% or when cotton cellulose was replaced by wood cellulose or celluosefrom bagasse or chemically treated celulose.

When the anmount of DMF-SO₃ complex added was that calculated to producea D.S. of below about 0.3-0.4, the resulting product was insoluble buthighly swellable in water.

EXAMPLE XIV

Cotton linter pulp wa hydrated by treatment with water in a WaringBlender as described above. The cellulose then was pressed out anddivided into 4 portions. One portion was dried in vacuo at 30°-40° Cwith continuous mixing down to a water content of about 20%. The otherthree parts were dried under the same conditions to 8-10%, 4-5%, and1-2% water, respectively. For the last sample the temperature wassomewhat increased. Amounts of 20 g. of each of the parts werenitrosated as described above with 30 g. of N₂ O₄. The reactions withsamples containing 8-10% and 4-5% moisture proceeded smoothly and werecomplete after about 20-30 minutes forming clear, viscous solutions. Thecellulose containing 20% moisture required about 35 g. N₂ O₄ and formeda clear solution soon after the 5 g. excess had been added. Thecellulose portion containing 1-2% moisture required a long time ofmixing and, even after the addition of a moderate excess, remainedsomewhat hazy and contained fibers.

Subsequent sulfations using DMF-SO₃ complex containing about 6 g. of SO₃in each case resulted in cellulose sulfates with a D.S. of about 0.6producing sparkling clear solutions in water when celluloses withmoisture contents of 20%, 8-10%, and 4-5% were used initially. Solutionsof the reaction product from cellulose with the lowest moisture content,however, were somewhat hazy and appeared to contain fibers.

Similar results were obtained when cotton linter pulp was replaced bywood cellulose or cellulose from vegetable hulls or bagasse, or when theDMF was substituted by DMAC, or when instead of the DMF-SO₃ complex, acomplex with dioxane, DMAC, DMSO, or the like was used.

In another identical experimental series, where 20 g. portions ofcellulose were nitrosated with about 20 g. of N₂ O₄ (about 25 g. of N₂O₄ required for the cellulose containing about 20% moisture) andsulfated with DMF-SO₃ complex containing about 10-12 g. of SO₃, productswith D.S. values of 1.1-1.2 were obtained, but otherwise results weresimilar.

The nitrosation and subsequent sulfation proceeded similarly smooth andresulted in sulfated products forming clear aqueous solutions when acommercial cotton linter pulp or wood cellulose with moisture contentsof between about 4-12% was used directly. If 5%, 10%, or 20% water wasadded to anhydrous cellulose at once just before the reaction, resultswere similar to those obtained under Example XII with anhydrouscellulose.

EXAMPLE XV

Five samples of cotton linter pulp (20 g. each) were nitrosated asdescribed above with about 30 g. of N₂ O₄ each and then sulfated withDMF-SO₃ complex containing the theoretical amounts of SO₃ calculated forD.S. values of about 0.4, 0.6, 0.8, 1.1, and 1.6. After neutralizationand isolation, the D.S. values of the products were found to be about0.4, 0.6, 0.8, 1.1, and 1.1, respectively. The same D.S. values of about1.0-1.1 were obtained also when the amount of N₂ O₄ was reduced to 25 g.or about 20 g. and the SO₃ was calculated for a D.S. of about 1.1 and1.6.

Cotton linter pulp (20 g.) which was nitrosated with 14 to 15 g. of N₂O₄ produced, after sulfation with a theoretical amount or a moderateexcess of SO₃, a product with a D.S. of about 1.5 to 1.6. If the N₂ O₄was increased to 17 or 18 g., a theoretical amount or an excess of SO₃produced a D.S. of 1.3 to 1.4. However, if for the nitrosation about 25g. of N₂ O₄ was used, theoretical amounts of SO₃ were sufficient toproduce D.S. values of between about 0.5 and 1.1. If less than about 10g. of N₂ O₄ was used for nitrosation, no complete sulfation was attainedwith DMF-SO₃ complex even when used in moderate excess. Substantiallysimilar results were obtained when, instead of cotton linter pulp, woodcellulose or bagasse was used.

EXAMPLE XVa

Carboxymethyl cellulose (10 g.) with a D.S. of about 1.0 was suspendedin about 500 ml. DMF, and 7.5 to 8.0 g. N₂ O₄ was introduced underexclusion of moisture and with strong agitation. The mixture formed alight green, viscous solution of carboxymethyl cellulose dinitriteester.

For the isolation and identification of the ester, the same procedurewas used as described under Example 1 for cellulose nitrite ester. Ifless N₂ O₄ was used for the nitrosation, the degree of nitrosation wascorrespondingly lower.

Similar results were obtained when methyl cellulose with a D.S. of 1.0and 1.5, hydroxypropyl cellulose with a D.S. of 0.8, acetyl alginic acidesters with a D.S. of 0.5 and 0.8, hydroxyethyl starch with a D.S. ofabout 0.2, partially hydrolyzed polyvinyl acetate with a D.S. of 0.4,acetyl pectic acid ester with a D.S. of 1.2, hydroxyethyl guar an locustbean gums with a D.S. of about 0.4 and 0.7, hemicellulose nitrate esterwith a D.S. of about 0.3 (as described in the German OffenlegungsschriftNo. 2,120,964), polyvinyl alcohol sulfuric acid ester with a D.S. of0.3, starch phosphate, carrageenan (free acid), xanthan gum (free acid),or gum karaya were nitrosated under similar conditions withstoichiometric amounts of N₂ O₄ to result in complete or partialesterification of the free hydroxyl groups.

Similar results were obtained when the DMF was replaced by DMAC,pyridine, isoquinoline, quinoline, and the like, or when NOCl instead ofN₂ O₄ was used provided that its molar amount was essentially tripled.Also, the reaction medium could contain substantial quantities of aninert solvent, such as ethyl acetate, ethyl formate, benzene, toluene,ethylene dichloride, acetone, methylethyl etone, and the like, withoutsubstantially changing the reaction.

EXAMPLE XVI

DMF (100 ml) was poured into a 250 ml two-neck round bottom flaskequiped with calcium chloride tube and magnetic stirrer. Then, 23 g. ofN₂ O₄ (1/4 mole) was added with stirring and cooling which resulted inthe formation of a deep green solution. To this solution, 12 g. absoluteethyl alcohol (about 1/4 mole) was added slowly with stirring. Duringaddition of the last ml, the solution became light yellow indicatingcomplete consumption of the N₂ O₄. Then, the solution was neutralized bythe addition of pyridine and subjected to fractionated distillation. Thefirst fraction was collected in a flask cooled with acetone dry ice andconsisted of about 18 g. of a yellowish liquid having a boiling point of17°-18° C. No ethyl alcohol was recovered during distillation.

Using the same conditions as in Example XVI, the ethyl alcohol wasreplaced by propanol, isopropanol, butanol, isobutanol, tertiary butylalcohol, amyl alcohol, isoamyl alcohol, and hexyl alcohol and 1/8 moleethylene glycol. On fractionated distillation, the corresponding nitriteesters were recovered in 80-90% yields with boiling points of about 57°C., 45° C., 77° C., 68° C., 63° C., 104° C., 99° C., 130° C., and 98°C., respectively. In no case was any alcohol recovered.

In another series of experiments, 15 g. of a low D.P. cellulose wassuspended in the 100 ml of DMF before the N₂ O₄ was added. Addition of23 g. of N₂ O₄ with strong stirring resulted in a cellulose trinitriteester solution. To this solution, alcohol under conditions and inamounts as described above (1 mole alcohol or 0.5 mole diol per mole N₂O₄) was added. Free cellulose separated and was removed. The filtratewas neutralized and distilled as described above and the correspondingalkyl nitrites were obtained in yields of 80-85% of the theory. Similarresults were obtained when, instead of cellulose, stoichiometric amountsof methyl cellulose, starch, alginic acid, or polyvinyl alcohol wereused.

In a third experimental series, to cellulose trinitrite ester solutinsobtained under conditions and in amounts as described above were addedslowly and with continuous stirring amounts of DMF-SO₃ complex to resultin mixed cellulose nitrite sulfuric acid esters having degrees ofsulfation of about 0.4, 0.8, and 1.1. To these ester solutions, alcoholwas added under conditions and in amounts as described above, thecellulose sulfuric acid ester precipitated by the addition of asufficient amount of acetone and removed, and the filtrate neutralizedwith pyridine and subjected to fractionated distillation. Thecorresponding alkyl nitrites were recovered in a purity and in yieldssimilar to those obtained from cellulose trinitrite ester solutionsabove.

EXAMPLE XVII

Cotton linter pulp (400 g.) having a moisture content of about 5-6% wasmixed with 2 1. of DMF in a double planetary mixer with cooling andunder exclusion of moisture, and 600 g. of N₂ O₄ was added over a periodof about 30 minutes to result in a cellulose trinitrite ester. Then, aDMF-SO₃ slurry in DMF containing about 200 g. of SO₃ was added slowlyover a period of about 30 minutes and mixing continued for another 10-15minutes. An amount of 485 g. of isobutyl alcohol was added slowly, andthe mixture was neutralized (pH 7-8) by the addition of an aqueoussolution of sodium carbonate or a slurry of sodium carbonate in asaturated solution or by the addition of dry sodium carbonate. Good andthorough mixing was required for this neutralization step, and generallythe presence of water produced better results. The temperature of thereaction mixture was maintained below about 20° C. throughout thereaction until neutralization was complete, and up to the neutralizationstep, the reaction was carried out under exclusion of moisture. Theneutral mixture was then pressed out or centrifuged, and if the solidswere too soft to be pressed out, some isopropanol was added to hardenthem sufficiently. The solids were suspended in about 60-70% aqueousisopropanol, pressed out again, dried, and milled. For higher purity,the solids were suspended in aqueous isopropanol a second and, ifnecessary, a third time before final drying and milling.

The filtrates were combined and subjected to fractionated distillationfor solvent recovery. One of the fractions distilled at about 66°-67° C.and was identified as isobutyl nitrite, the yield being over 80%. Thebrown, crystalline residue from distillation contained the theoreticalamount of sodium nitrite. An aliquot of it was purified byrecrystallization.

In other identical experiments, the isobutyl alcohol was replaced byn-propanol, amyl alcohol, and ethylene glycol. Instead of isobutylnitrite, the corresponding nitrite esters of n-propanol, amyl alcohol,or ethylene glycol were recovered, but otherwise results were similar.In another similar experiment where the isobutanol was replaced by anequivalent amount of water, similar results were obtained, but theresidue from the solvent recovery contained equivalent amounts of sodiumnitrite and sodium nitrate in theoretical yields. Part of the residuewas recrystallized to result in a purified salt mixture.

The sodium cellulose sulfate had a D.S. of 1.0-1.1, and a 1% aqueoussolution had a viscosity of 1500-2000 cps.

In another experimental series, products were obtained under similarconditions, but the amount of SO₃ used for the sulfation was reduced toobtain products with D.S. values of about 0.4, 0.6, and 0.9. These D.S.values were attained with the theoretically calculated amounts of SO₃,and 1% aqueous solutions of the products had viscosities ranging betweenabout 5000 and 2000 cps. In another experiment, the amount of N₂ O₄ wasreduced to about 300 g. and that of SO₃ increased to about 300 g. toresult in sodium cellulose sulfate esters with a D.S. of 1.5-1.6 having1% aqueous viscosities of about 600-700 cps.

Other cellulose materials, such as wood cellulose or cellulose fromvegetable hulls were used with equal success, but the final products hada somewhat lower solution viscosity than those from high D.P. cottonlinter pulp. Also, neutralization could be carried out equally well withcarbonates, bicarbonates, and hydroxides of the other alkali metals,such as lithium and potassium, of alkali earth metals, such as magnesiumand calcium, and of manganese, cobalt, and nickel and with ammoniumhydroxide and amines. In the case of the alkali metals, carbonates andbicarbonates are preferred to the hydroxides because of the highalkalinity of the hydroxides and the danger of degradation.

Also an integral part of my invention is the process of making films,fibers, and other shaped articles by (1) preparing a solution or pastecontaining the labile nitrite ester of one or more polyhydroxypolymersor a solution or paste of both one or more polyhydroxypolymer nitriteesters and one or more polymers lacking hydroxyl groups and (2)contacting said solution or paste with a protic solvent in the presenceof an acidic catalyst to cause (a) regeneration of thepolyhydroxypolymer and, essentially simultaneously, (b) separation ofboth the regenerated polyhydroxypolymers and the polymers lackinghydroxyl groups in such a manner that films, fibers, or other shapedarticles are obtained.

The first step of the process consists of making the nitrite ester ofthe polyhydroxypolymer or polyhydroxypolymer mixtures as previouslydescribed. As the polyhydroxy compound, any polymer containing asubstantial number of hydroxyl groups is suitable. This includespolysaccharides typified by cellulose irrespective of its source,alginic acid, pectic acid, pectin, hemicellulose, gum arabic, guar gum,locust bean gum, gum karaya, and the like, polysaccharide derivativesstill containing a substantial number of hydroxyl groups as typified bycarrageenan and other polysaccharide sulfates, methylcellulose,carboxyalkylcellulose, hydroxyalkylcellulose, hydroxyalkylguar and otherpolysaccharide ethers, partially acetylated or generally esterifiedpolysaccharides, partially nitrated or sulfated polysaccharides such asdescribed previously, and the like, and synthetic polyhydroxypolymerstypified by polyvinylalcohols with various degrees of saponification andcopolymers containing vinylalcohol.

To the suspension of the polyhydroxypolymer(s) in one of the specifiedsolvents or solvent mixtures, enough dinitrogentetroxide and/ornitrosylchloride is added in gaseous or liquid form or as a solutionpreferably in one of the previously mentioned solvents to obtain ahighly esterified nitrite ester of the polyhydroxypolymer(s). Thereaction temperature should be maintained below about 50° C. andpreferably below about 30° C. If the temperature increases to aboveabout 60° C. over an extended period of time, some nitration of thepolyhydroxypolymer may occur. This however, may not have anydisadvantageous consequences in the subsequent film or fiber formation,and, in some instances, it may be even desirable.

Films, fibers, and other shaped articles of the unmodifiedpolyhydroxypolymer(s) are obtained by bringing the paste or solution ofthe nitrite ester(s) into the desired shape and then contacting it inthe presence of an acidic catalyst with a protic solvent in which theresulting polyhydroxypolymer(s) is (are) insoluble. Films, for example,can be made by spreading the solution on a glass plate and treating itwith a protic solvent while fibers are obtainable by extruding thesolution into the protic solvent. The shaped objects then may beimmersed in and washed with more solvent and dried. To neutralizeresidual catalyst, a small amount of a base, such as alkali or ammoniumhydroxides or an amine, may be added to one of the washes if so desired.

Although it is possible to first isolate the polymeric nitrite ester andthen redissolve it for the purpose of film and fiber formation, it ispreferred to use the reaction solution containing the nitrite esterdirectly. The preferred acidic catalyst is a mineral acid, such ashydrochloric, sulfuric, nitric, phosphoric acids, and the like, however,relatively strong organic acids are suitable also. If anN,N-dialkylacylamide had been used as the proton acceptor fornitrosation of the polyhydroxypolymer, the nitric acid and/orhydrochloric acid formed simultaneously as a by-product is sufficient toserve as a catalyst. However, if a weak tertiary amine had been used forthis purpose, enough catalyst should be added to make the mixtureacidic. The catalyst must be anhydrous to avoid removal of nitritegroups prior to the treatment with the protic solvent. Of course, asufficient amount of catalyst may be added to the protic solvent insteadof to the nitrite ester solution, and film or fiber formation isachieved with similar success. In the case of a nitrite ester solutionwhere a N,N-dialkylacylamide is used as the proton acceptor, it may beadvantageous to neutralize or slightly alkalize the solution toeliminate the reactivity to moisture and add the catalyst to the proticsolvent. The protic solvent to be used depends largely on thepolyhydroxypolymer to be regenerated. For most polysaccharides andsynthetic polyhydroxypolymers, anhydrous or aqueous alcohols, such asmethanol, ethanol, isopropanol, and the like, are required because ofthe water solubility of these polymers. In the case of cellulose or amixture of a substantial amount of cellulose and anotherpolyhydroxypolymer, water may be used as well. At times, it isadvantageous, i.e., the polymer separation is improved, if the proticsolvent is mixed with another type of solvent provided that this secondsolvent does not inactivate the catalyst and that it is completelymiscible with the protic solvent as well as with the nitrite estersolvent.

In addition to the polyhydroxypolymer mitrite esters, other solublepolymers may be added to the nitrite ester solution. This may be done bydissolving the polymer directly in the reaction mixture containing thenitrite ester or by pre-dissolving the polymer in a suitable solvent andadding the resulting solution to the nitrite ester solution or viceversa. Although, because of simplified solvent recovery, it is preferredto use the same solvent as contained in the nitrite ester reactionmixture, other aprotic solvents, such as chlorinated hydrocarbons,hydrocarbons, alkylesters, aromatics, acetonitrile, dioxane, and thelike, may be used for pre-dissolving the polymer provided that suchsolvent is compatible, i.e., completely miscible, with the nitrite esterreaction solution and with the protic solvent to be contacted withsubsequently. Of course, if the nitrite ester solution is neutral oralkaline, i.e., does not contain the acidic catalyst, such solvent mayalso be protic as typified by alcohol and water. In this case, theacidic catalyst is added to the protic solvent to be used subsequentlyfor the regeneration of the polyhydroxypolymer and the separation of thepolymer mixture in the form of certain shaped articles. The type ofadditional polymer which may be added to the nitrite ester solution maybe any polymeric compound which either does not contain any hydroxylgroups or the hydroxyl groups of which are essentially completelysubstituted. Polymers of that type are synthetic polymers typified bypolyacrylic esters, methacrylic esters, polyacrylonitrile, and otheracrylics, polyvinylesters, -ethers, and -halides, vinyl and acryliccopolymers, polystyrene and copolymers, ethylene copolymers, propylenecopolymers, phenolics, polyamides such as nylon, polyethers, polyesters,polyalkyleneglycols, and others and highly substituted polysaccharidestypified by their nitrate, acetate, propionate, and other esters, theirmethyl, ethyl, and other ethers, and the like. The only requirements arethat such polymer is soluble in one or more of the above solvents, thatit is compatible with the polymeric nitrite ester solution, and that itcan be separated simultaneously with the polyhydroxypolymer by theproper choice of the protic solvent or the solvent mixture containingthe protic solvent. A limited amount of an additive, such as aplasticiser, or of a liquid lower molecular weight polymer may be addedalso provided, of course, that it is retained in the film or fiber andnot leached out during film or fiber formation. Films, fibers, and othershaped objects are obtained by contact with a protic solvent in thepresence of an acidic catalyst in the way described above. As alreadymentioned, the choice of the protic solvent depends on the polymermixture, and it should be selected in such a way that, on contact,regeneration of the polyhydroxypolymer and separation of both thepolyhydroxypolymer and the polymer lacking hydroxyl groups occuressentially simultaneously. Of course, prior to contact with a proticsolvent, part or most of the polymer solvent, especially in the case ofa low boiling solvent, may be evaporated and, thus, the polymerconcentration increased. This often improves fiber and film formation.

The shaped articles obtainable by my process consist of homogeneous andintimate mixtures of the polymers originally present in the polymericnitrite ester solution. Thus, they may consist of only onepolyhydroxypolymer, or they may consist of a combination of severalpolyhydroxypolymers or of one or more polyhydroxypolymers and one ormore polymers lacking hydroxyl groups. Of course, if desired, unreactedcellulose fibers may be included in such articles by suspending thedesired amount of cellulose fiber in the polymer solution prior to filmor fiber formation. In combination of several polymers, the polymerratio can be chosen arbitrarily, and the weight percentage of anypolymer may vary between about 0.1 and 99.9.

Shaped articles containing acidic polymers, such as polymeric sulfuricor phosphoric acid esters, polyuronic acids, polyacrylic acid, and thelike, may be modified further by neutralizing with various bases, suchas alkali, ammonium, and alkali earth hydroxides and the variousprimary, secondary, and tertiary amines. Also, the alkali salt of suchacidic compound may be treated with a quaternary ammonium halideresulting in an exchange of the alkali ion by the quaternary ammoniumion. This will produce property changes of the shaped object, such asincreased or reduced water sensitivity or even water repulsion dependingon the ion selected.

The usefulness of the shaped articles, particularly films and fibers, isobvious and need not be demonstrated. Films of cellulose, celluloseacetate, and cellulose nitrate, for example, are used in packagingmaterial, membranes, and the like, films of other polysaccharides areused as food packaging materials, and fibers of cellulose, polyesters,polyamides, and other polymers are used in the manufacture of, forexample, textiles. The novel combination of several polymers asdescribed in this invention, such as cellulose - polyester, cellulose -polyvinylalcohol, polyvinylalcohol - nylon, and the like, in the samefilm or fiber will combine some of the advantages of the individualpolymers but also will add new properties, such as possibly higherstrength, increased flexibility, improved dyability, antistaticproperties, and the like. The incorporation of a negatively chargedpolymer in, for example, cellulose or cellulose acetate films may beuseful in their application as osmotic membranes or, because of theadded protein reactivity, in the meat industry as, for example, sausagecasing and in medical applications.

The following examples illustrate specific preferred embodiments of thisinvention and are not intended to be limiting.

EXAMPLE XVIII

High molecular weight cotton linter pulp (10 g.) was suspended in 300ml. DMF and, under exclusion of moisture, 16 g. dinitrogentetroxide wasintroduced slowly and with mechanical agitation. Strong agitation wascontinued until a clear highly viscous solution was obtained. Part ofthe solution was spread evenly on a glass plate in a low humiditychamber and then sprayed with anhydrous or aqueous methanol, the filmremoved, blotted between filter paper, immersed in and washed withmethanol, and dried. The film was clear and strong. Fibers of highclarity and strength were obtained by extruding the solution throughfine nozzles into methanol, washing the resulting fibers with freshmethanol, and drying. If droplets of the solution were dropped intomethanol, washed with methanol, and dried, the product was obtained inthe form of granules. The granular size depended on the concentration ofthe cellulose in the solution and on the size of the droplets.

Similar results were obtained when a lower molecular weight cellulose orcellulose from other sources was used or when the cellulose was replacedby polyvinyl alcohol, starch, hemicellulose, guar gum, locust bean gum,alginic acid, pectic acid, hydroxyethyl cellulose, methyl cellulose witha D.S. of about 1.5, or propylene glycol alginate.

EXAMPLE XIX

Cotton linter pulp (5 g.) and 5 g. polyvinyl alcohol were suspended in200 ml. DMF, and sufficient dinitrogentetroxide was introduced to resultin a clear viscous solution on prolonged mixing. Films, fibers, andgranules were obtained from this solution as described under ExampleXVIII. Substitution of nitrosyl chloride for dinitrogentetroxide or of amixture of DMF and benzene and DMF produced similar results.

The same results were obtained when the ratio of the two polymers waschanged to 8 : 2 or 2 : 8 and/or when other polymer mixtures were used,such as cellulose - starch, cellulose - cellulose sulfuric acid, ester,cellulose - carrageenan, cellulose - alginic acid, cellulose - pecticacid, cellulose - guar gum, cellulose - gum arabic, starch - alginicacid, starch - pectic acid, and when mixtures of three or more of theabove polymers were used.

If the methanol used for separating films and fibers was replaced byethanol, isopropanol, aqueous acetone, and methanol - acetone mixtures,films, fibers, and granules of the polymers were obtained equally well.

Films, fibers, and granules containing an acidic polyhydroxypolymer wereneutralized by immersing in aqueous or anhydrous methanol containingammonium, sodium, or potassium hydroxides, propylamine, dibutylamine,trilaurylamine, or triethanolamine. Softness, flexibility, watersensitivity, and other characteristics of the products depended to someextent on the base used for neutralization.

EXAMPLE XX

Cellulose (10 g.) was suspended in 200 ml. DMF and about 15 g.dinitrogentetroxide introduced to obtain a clear solution. A solution of10 g. of polyvinyl acetate in 50 ml. ethylacetate was added, and fromthis mixture, films and fibers were prepared in a manner described underExample XVIII. Films and fibers were obtainable equally well whenstarch, alginic acid, guar gum, or hydroxypropyl cellulose wassubstituted for cellulose and/or cellulose nitrate, cellulose acetate,polyacrylic ester, or polymethacrylic ester substituted for polyvinylacetate.

In another experiment, the polyvinyl acetate solution was replaced by asolution of 10 g. of nylon in hot DMF and, in a further experiment, by10 g. polyethylene glycol in DMF, and films and fibers were preparedwith equal success.

Changing the ratios of the polymers in the solutions did not adverselyaffect film and fiber formation.

EXAMPLE XXI

Polyvinyl alcohol (10 g.) was suspended in 80 ml. DMAC, about 10 g.dinitrogentetroxide introduced with mechanical stirring and underexclusion of moisture, and stirring continued until a clear solution wasobtained. Then, a solution of 10 g. polyacrylonitrile in 50 ml. DMAC wasadded and the resulting clear solution of the polymer mixture used forfilm and fiber formation. A mixture of benzene - isopropanol - water wasused for separation of the polymers, and isopropanol was used forwashing.

Essentially similar results were obtained when the polyacrylonitrilesolution was replaced by solutions of methyl vinyl ether - maleicanhydride copolymer, polyester, polyvinyl chloride, polyketone, phenolicresin, ethylene - acrylic acid copolymer, or polystyrene, or by asolution of two of such polymers and/or polyvinyl alcohol wassubstituted by guar gum or a mixture of cellulose and starch.

EXAMPLE XXII

Hydroxyethyl cellulose (10 g.) was solubilized in a mixture of 85 ml.DMF and 15 ml. pyridine by introducing a sufficient amount ofdinitrogentetroxide and the resulting solution mixed with a solution ofpolyvinyl hydrogenphthalate (10 g.) in DMAC. The resulting solution ofthe two polymers then was spread on glass plates and the plates immersedin aqueous ethanol containing hydrochloric acid in excess to the amountof pyridine on a molar basis. The films then were removed, washed withethanol, kept in ethanol containing a small amount of ammonia, anddried.

EXAMPLE XXIII

Cellulose (10 g.) was solubilized in a mixture of 50 ml. DMF and 50 ml.ethyl acetate with a sufficient amount of dinitrogentetroxide, and asolution of 12 g. cellulose acetate in 100 ml. ethyl acetate was added.The resulting solution was spread on glass plates in a low humiditychamber, most of the solvent removed by evaporation under reducedpressure, and the plates immersed in methanol. The films were washedwith methanol and dried.

Similar results were obtained when polyvinyl acetate was substituted forcellulose acetate and/or alginic acid for cellulose.

I claim:
 1. A process for simultaneously preparing a sulfate ester ofcellulose and an alkyl nitrite comprising:reacting a nitrite ester ofcellulose with sulfur trioxide or a complex thereof at a reactiontemperature of about 0° to about 25° C. to obtain a mixednitrite:sulfate ester of cellulose; said reaction being carried out inthe presence of dinitrogen tetroxide; reacting said mixed ester with analcohol containing up to about 10 carbon atoms; said alcohol reactingwith the nitrite groups in said mixed ester and also with dinitrogentetroxide to produce an alkyl nitrite and to free the mixed ester ofnitrite groups.
 2. A process for simultaneously preparing a sulfateester of cellulose and a mixture of an inorganic nitrite with aninorganic nitrate, said process comprising:reacting a nitrite ester ofcellulose with sulfur trioxide or a complex thereof at a reactiontemperature of about 0° to about 25° C. to obtain a mixednitrite:sulfate ester of cellulose; said reaction being carried out inthe presence of dinitrogen tetroxide; adding water to said reactionmixture, and neutralizing the sulfuric acid ester of cellulose throughaddition of a base.
 3. A process for preparing a sulfate ester ofcellulose in which the sulfate ester groups are substantially uniformlydistributed among the polymer units of the cellulose, said processcomprising:reacting cellulose which contains from about 4 to about 12percent by weight of water with dinitrogen tetroxide or nitrosylchloride to obtain a cellulose nitrite ester in which the nitrite estergroups are substantially uniformly distributed among the polymer unitsof the cellulose; said reaction being carried out in the presence of aswelling or solubilizing solvent for the resulting cellulose nitrite ana proton acceptor; said water being substantially uniformly distributedthrough the cellulose reactant; said reaction being carried out withagitation at a reaction temperature below about 50° C.; said solventbeing present in an amount sufficient to provide at least about theeeparts by weight of solvent for each part of cellulose; reacting saidnitrite ester with sulfur trioxide or a complex thereof at a reactiontemperature of about 0° to about 25° C. to obtain a mixednitrite:sulfate ester of cellulose; reacting said mixed nitrite:sulfateester with a protic solvent to remove residual nitrite ester groups fromsaid cellulose, and reacting said cellulose with a base to neutralize orslightly alkalize said cellulose and to obtain said cellulose sulfate inthe form of its salt.
 4. The process of claim 3 whereinthe degree ofnitrite substitution of the nitrite ester is about 2 to below about 3and the degree of sulfate substitution of the sulfate ester ranges up toabout 1.1
 5. The process of claim 3 whereinthe degree of nitritesubstitution of the nitrite ester is less than about 2 and the degree ofsulfate substitution of the sulfate ester is greater than about 1.1. 6.A process for preparing a sulfate ester of cellulose in which thesulfate ester groups are substantially uniformly distributed among thepolymer units of the cellulose, said process comprising:treatingcellulose which contains in excess of about 4 percent by weight of waterdistributed substantially uniformly throughout the cellulose with ahighly polar aprotic solvent to reduce the water content in saidcellulose to less than about 4 percent by weight of the cellulose;reacting the treated cellulose with dinitrogen tetroxide or nitrosylchloride to obtain a cellulose nitrite ester in which the nitrite estergroups are substantially uniformly distributed among the polymer unitsof the cellulose; said reaction being carried out in the presence of aswelling or solubilizing reaction solvent for the cellulose nitriteester and a proton acceptor; said reaction being carried out withagitation at a reaction temperature below about 50° C.; said reactionsolvent being present in an amount sufficient to provide at least aboutthree parts by weight of solvent for each part of cellulose; reactingthe nitrite ester with sulfur trioxide or a complex thereof at atemperature of about 0° to about 25° C. to obtain a mixednitrite:sulfate ester of cellulose; reacting said mixed nitrite:sulfateester with a protic solvent to remove residual nitrite ester groups fromsaid cellulose, and reacting said cellulose with a base to neutralize orslightly alkalize said cellulose and to obtain said cellulose sulfate inthe form of its salt.
 7. The process of claim 6 whereinthe degree ofnitrite substitution of the nitrite ester is about 2 to below about 3and the degree of sulfate substitution of the sulfate ester ranges up toabout 1.1
 8. The process of claim 6 whereinthe degree of nitritesubstitution of the nitrite ester is less than about 2 and the degree ofsulfate substitution of the sulfate ester is greater than about 1.1.